Coaxial arrangement of tubular members, and spacer structure for such arrangements

ABSTRACT

A coaxial arrangement for coolable cables or the like, comprises inner and outer tubular members which form a longitudinally extending, annular interspace between each other, one or both these members being contactable by coolant passing through the cable during operation. The annular interspace is secured by longitudinally spaced spacer structures of poor heat-conducting material. Each of the spacer structures is in contact with the respective tubular members at only small areas and has a ring portion surrounding the inner tubular member when in assembled condition. The ring-shaped portion has inwardly directed and angularly spaced bosses or little protrusions which face and contact the inner tubular member when the arrangement is in assembled condition. Three spoke members are joined with and protrude in a radially outward direction from the ring portion so as to engage the outer tubular member of the arrangement when assembled. The three spoke members are 120* peripherally spaced from each other. Each spacer structure is composed of a plurality, preferably three component members, each component member carrying one of the three spoke members.

United States Patent [72] Inventors Hubert Kdhler;

Irltz Schmidt, both 01 Erlangen, Germany [21 Appl. No. 57,085 22] FiledJuly 22, 1970 H] Patented Sept. 14, 1971 I73] Auignee SiemensAlrtiengeaellachaft Berlin, Germany [32] Priority July 25, 1969 [33]Germany [31] P 19 37 795.8

[54] COAXIAL ARRANGEMENT 0E TUBULAR MEMBERS, AND SPACER STRUCTURE FORSUCH ARRANGEMENTS Claims, 2 Drawing Figs.

[52] U.S.Cl 174/15, 174/D1G. 6, 174/28 [51] lnt.Cl 1101b 7/34 [50] Fieldof Search 174/28, 29, 15,15 R,D1G. 7; 138/114, 1

[56] References Cited UNITED STATES PATENTS 3,390,703 7/1968 Matlow138/114 3,501,581 3/1970 Edwards... 174/15 12, 6/1279 -.v 2. 1.7.4LL

3,529,6ii 9/1970 Kafka Primary ExaminerLewis H. Myers AssistantExaminerA. T. Grimley Attorneys-Curt M. Avery, Arthur E. Wilfond,Herbert L. Lerner and Daniel J Tick ABSTRACT: A coaxial arrangement forcoolable cables or the like, comprises inner and outer tubular memberswhich form a longitudinally extending, annular interspace between eachother, one or both these members being contactable by coolant passingthrough the cable during operation. The annular interspace is secured bylongitudinally spaced spacer structures of poor heat-conductingmaterial. Each of the spacer structures is in contact with therespective tubular members at only small areas and has a ring portionsurrounding the inner tubular member when in assembled condition. Theringshaped portion has inwardly directed and angularly spaced bosses orlittle protrusions which face and contact the inner tubular member whenthe arrangement is in assembled condition. Three spoke members arejoined with and protrude in a radially outward direction from the ringportion so as to engage the outer tubular member of the arrangement whenassembled. The three spoke members are peripherally spaced from eachother. Each spacer structure is composed of a plurality, preferablythree component members, each component member carrying one of the threespoke members.

I COAXIA L ARRANGEMENT F TUBULAR MEMBERS, AND SPACER STRUCTURE FOR SUCHARRANGEMENTS Our invention relates to coaxial arrangements of tubularmembers for cryogenically or otherwise coolable cables or the like. In amore particular aspect, our invention concerns a spacer structure ofpoor heat-conducting material for main taining in such coaxialarrangements the required annular and longitudinally extendinginterspace between inner and outer tubular member, the space structurebeing such as to contact the tubular members at only small areas oftheir respective wall surfaces.

Deeply cooled, particularly superconducting cables offer considerableadvantages for the transmission of high quantities of electrical energy.The electrical conductors of such cables may consist of electricallynormal conductivity and preferably highly pure metals, for examplehigh-purity aluminum, whose ohmic resistivity is considerably smaller atlow temperature than at normal room temperature (C.). Especially wellsuitable for such cables are superconducting metals whose ohmicresistance completely vanishes when cooling the conductor to atemperature below a critical temperature depending upon the particularsuperconductor material being used. Suitable as superconductingmaterials for such purposes are particularly the metals niobium and leadas well as the socalled high-field superconducting materials, forexample superconducting alloys of niobium and titanium, or niobium andzirconium, as well as such superconducting compounds as niobium-tinNb,sn For electrical stabilization, the superconductors may be joinedwith electrically parallel-connected metals that exhibit electricallynormal conductivity at the operating temperature of the superconductors,the parallelconne cted normal conductivity metals being in goodelectrically arid good thermally conducting contact with thesuperconductors for which purpose the superconductors may be embedded inthe normal conductivity metals.

Conductors of electrically normal conductivity metals are cooledpreferably with liquids whose boiling temperature is below approximately150 K., such as liquid hydrogen, liquid nitrogen, liquid natural (earth)gas or cold gases of correspor'idingly low temperatures. The cooling ofsuperconductors, referring to the superconducting materials presentlyavailable commercially, is effected virtually only by liquid helium orcold, gaseous helium.

in known cables of he general types mentioned, the conductors arearranged within a tube filled with, or traversed by coolant. The tubeitself may also be electrically conducting or be coated with aconducting layer. The cooling power required for the cooling of theconductor should be kept as small as feasible and coolant losses shouldbe avoided as much as feasible. For these reasons the conductors and thecoolant used for cooling the conductors must be thermally insulated fromthe environment of the cable. As a rule, such thermal insulation isprovided with the aid of tubular envelopes which surround the conductorand the tube enveloping the conductor. The tubular envelopes, forexample, may be designed as radiation shields and may be cooled by asecond coolant having a higher temperature than the coolant used forreducing the temperature of the conductor. The interspaces between thetubular envelope, unless filled or traversed by coolant, are preferablyevacuated and may contain several additional layers of poorheat-conducting material and reflecting metal layers. These layers, forexample, may consist of polyethylene terephthalate foils which may becoated with reflective layers of aluminum.

The tube surrounding the conductors and the further tubes surroundingthe first tube are braced against each other by spacer structures. In aknown superconducting cable such spacer structures between the tubularradiation shield and the conductor system consist of series of glassdiscs or ceramic discs (E. C. Rogers and E. R. Edwards in ElectricalReview, Vol. 81, 1967, pages 848 to 851). With such disc-shaped spacers,however, the areas of engagement with the tubes whose spacing is to besecured, is relatively large so that the Aside from deeply cooled orcryogenically cooled cables, 1

spacer structures of poor heat conducting material between coaxial tubesare also desirable in cables or du'cts for the transportation of liquidlow-boiling gases in which a tube surrounded by further tubes, serves totransport the liquified gases.

It is an object of our invention to further improve such coaxialarrangements of tubular members for cryogenically coolable cables or theabove-mentioned analogous other purposes; and it is also an object ofthe invention to devise a spacer structure of improved design and easeof assembling suitable for use in such coaxial arrangements. 5

Another, more specific object of our invention, relating to theabove-mentioned coaxial arrangement of tubular members and/or spacersfor such arrangements, is to further minimize the areas of engagementbetween the spacer and the tube walls.

It is also an object of the invention to design a spacer for use 1 twith coaxial tubular arrangements in such a manner that the connectingpaths between the respective inner and outer tubular members ofrespectively different temperatures are greatly extended.

To achieve these objects, and in accordance with our invert tion, weprovide spacer structures of poor heat conducting material which areaxially spaced from each other in the longitudinally extending, annularinterspace between inner and outer tubes, each spacer having a ringportion which s'urrounds the inner tubular member when. the coaxialarrangement is in assembled condition and which has inwardly directedbosses or other protrusions angularly spaced from each other for facingand contacting the inner tubular member in assembled condition. Thespacer structure surrounds the" entire periphery of the inner tube andis equipped with three spoke members. These are joined with the ringportion and protrude therefrom in a radially outward direction forengagement with the inner periphery of the outer tubular member when thearrangement is in assembled condition. The three spoke members areangularly spaced about l20 from each other and are preferably spacedabout 60from the abovementioned bosses.

In a coaxial arrangement of tubes, a spacer structure according to theinvention affords the advantage that the bosses, angularly spaced aboutl20from each other, and the spoke members, also spaced about from eachother, coact in securing reliable three-point bracing of the tubesrelative to each other, while simultaneously the areas of engagementbetween spacer and tubes are kept extremely small since the inner tubetouches the spacer structure only at the bosses and the outer tubetouches the spacers only at the outward end of the spoke-shapedsupporting elements. Since preferably the spoke-shaped members arespaced, angularly about 60from the bosses, the longest feasible paths ofthermal connection between inner tube and outer tube are attained.

To facilitate mounting and assembling, the spacer structure ispreferably made divisible. We prefer composing each spacer structure ofthree component parts of which each extends along about one-third of theinner-tube periphery.

In a preferred embodiment of such a spacer, and in accordance with morespecific features of our invention, a long connecting path between thetwo tubes with the aid of a threecomponent spacer is achieved by havingthe ring portion of each component part constituted by two ring elementswhich extend parallel to each other along one-third of the periphery andwhich carry above-mentioned protrusions or bosses, each of the threecomponent parts being provided with one of the spoke members, thismember having a V-shaped configuration. The ends of the ring elementsare joined with each other by respective bridge elements extendingapproximately parallel to the longitudinal axis of the tubes. Each ofthe two legs of the V-shaped spoke member is joined with one of therespective two ring elements, preferably at the middle of the ringelement.

In this preferred embodiment of the spacer structure, the bridge elementat one end of the ring elements in each component part of the spacer ispreferably provided with two bossshaped protrusions and has a notchextending along the bridge element on the side facing away from theinner tube, whereas the bridge member at the other end of the ringelement has an extension at the side facing away from the inner tube.The notches and extensions of the peripherally adjacent parts of thespacer structure are engageable with each other in tongueand-groovefashion. This has the advantage that each component part of the spaceris in touch with the inner tube through the bosses at only one end ofthe ring elements, whereas the same spacer part is supported at theother end of its ring elements upon the next adjacent spacer part.

The component parts of the spacer are suitably fastened on the innertube, preferably by means of a filamentary member such as a band orwire, which should consist of poor heat-conducting material, for examplea band of glass, silk or a steel wire.

The above-mentioned and further objects, advantages and features of ourinvention will be described in the following with reference to anembodiment of a coaxial cable structure according to the inventionillustrated by way of example'on the accompanying drawing in which:

FIG. 1 shows schematically and in cross section a superconducting cablewith two different embodiments of a spacer according to the invention;and

FIG. 2 shows in schematical perspective a component part of a spacerstructure according to a preferred embodiment of the invention.

Referring to FIG. I, the superconductive cable is provided with a hollowconductor 1 which can comprise, for example, a copper matrix 2 having aplurality of imbedded niobium titanium conductors 3. The conductor 1 issurrounded by a tube 4 made, for example, of stainless steel and throughwhich liquid helium streams during operation of the cable. Liquid heliumcan also flow within the hollow conductor 1 during operation of thecable. The tube 4 is surrounded by a second tube 5 made for example ofaluminum and forming a radiation shield. Second tube 5 is constructed intwo parts to facilitate assembly. Two tubes 6 of smaller diameter arejoined with tube 5 and carry liquid nitrogen during operation of thecable for cooling the radiation shield. Tube 7 is provided as an outercovering and surrounds tube 5. Tube 7 is also constructed in two partsand can be made, for example, of stainless steel. The two parts of tube7 are joined together vacuum tight by a welded seam at location 8.During operation of the cable, the intermediate spaces between tubes 4and 5 and tubes 5 and 7 are evacuated to obtain a thermal insulation.For additional thermal insulation, several layers 9 of poorheat-conductive material are disposed in the intermediate spaces, suchmaterial consisting of, for example, aluminum coated polyethyleneterephthalate foil or glass fiber material having aluminum foil disposedtherein.

Spacers l and 11 of poor heat-conductive material are provided betweenthe tubes 4 and and tubes 5 and 7 respectively, each of the spacersbeing constructed of three parts joined together. One part of spacer isillustrated in FIG. 2. The spacer 10 has a ring-shaped portion whichsurrounds the tube 4; this portion comprising the respective ringsegments 12 of the component parts. Each of the ring segments formsapproximately a third of the ring. On the sides of the component partsfacing the tube 4, there are provided bosses 13 located at 120 intervalsfor supporting the tube 4. In addition, the spacer 10 has threespokelike supporting portions 14 directed radially to the tube 5. Eachcomponent part of the spacer 10 has a supporting element 14 and in theassembled spacer, the elements 14 are spaced from each other and 60 fromthe protrusions 13.

As illustrated in FIG. 2, each component part of the spacer 10 comprisestwo ring segments 12 arranged next to each other which form aboutone-third of the circular ring. Struts l5 and 16 join the ends of thering segments and are disposed approximately parallel to thelongitudinal axis of the cable. The spokelike support elements 14 areconstructed in a V- shaped configuration and each leg 17 of the supportelement 14 is positioned at the center of the corresponding ring segment12.

The side of the one strut 16 facing the inner-lying tube is providedwith two bosses 13, the strut 16 being at one end of the two ringsegments 12. On the side of strut 16 facing away from the inner-lyingtube, there is provided a notch 18. The strut 15 at the other end of thetwo ring segments 12 has on its side facing away from the inner-lyingtube, an extension 19 constructed to accommodate the notch 18. Asillustrated in FIG. 1, notch and extension hold two neighboringcomponent parts of the spacer 10 within each other and so support eachother. The tubes 4 and 5 are supported against radial displacement bymeans of the bosses 13 and the spokelike support elements 14 in the formof a three point support arrangement. Since on each strut 16 of theindividual component part there are two bosses 13, the inner-lying pipeis protected against tipping by what collectively constitutes asix-point supporting arrangement. The upper edge of the V-shapedsupporting element l4 directed toward the outer lying pipe 5 isadvantageously constructed as a cutting means, so that when the poorheat-conductive foil 9 is wound about the tube 4, the cutting means caneasily press through this foil material. The foil 9 then lies tightagainst the supporting element I4, so that the heat-insulating effect ofthe foil is practically not interrupted.

The three component parts of the spacer 11 disposed between the innerlying tube 5 and the outer lying tube 7 have a configuration similar tothat of the spacer 10. Because of the nitrogen tubes 6 which are joinedto the tube 5, the form of the individual component parts of spacer IIare somewhat modified. The ring segments of the component part 20 have aband, so that the latter has no contact with the nitrogen tube 6. Thespokelike support elements of the component parts of the spacers 10 and11 lying above when the cable is in operative position can also beconstructed somewhat shorter than the spokelike support elements of theother component parts, so that there is no direct contact between thespokelike support elements of upper-lying component parts and the tubes5 and 7 respectively. The support elements cannot be omitted from thesecomponent parts because, with a displacement of the tube in the radialdirection, these supporting elements must perform their function.

Along the length of the cable of FIG. 1 there are provided a row ofspacers l0 and 11 spaced from each other. The poor heat-conductingtension bands used to secure the component parts of the spacers on thetubes 4 and 5 are not shown so that a better view is afforded. Forexample, the bands can be wound around the touching struts ofneighboring component parts such that the bands do not touch the innerlying tube.

Other embodiments of spacers of the invention can deviate in detailsfrom the preferred embodiment illustrated in FIGS. 1 and 2. For example,the spacers can consist of a unitary member rather component parts,however, this construction requires that the spacer be pushed on thetube. In addition, there is the possibility that instead of two ringsegments 12 of a component part, there be provided only a single ringsegment which has struts at its ends corresponding to the struts 15 and16. Instead of the V-shaped supporting element 14, there can be provideda conelike supporting element. Such an embodiment will have as a rule asomewhat lower strength than the construction illustrated in FIGS. 1 and2. The V-shaped support elements are practical, especially, formechanical requirements of the cable in the longitudinal direction. Suchmechanical requirements occur when the cable cools off, since withcooling, contraction occurs in tube 5 serving as the radiation shieldand, to an even greater extent, in the tube 4 through which heliumpasses, whereas the tube 7 which is at ambient temperature does notundergo a change in length. Because of this contraction produced bycooling, the individual tubes move against each other in a directionalong the longitudinal axis of the cable.

Ceramic materials with small heat-conductivity and high immunity totemperature changes are especially suitable as a material for thespacers. Examples of such materials are sirconium-aluminum-silicate,casting porcelain or glass ceramics with small expansion coefficients.In this connection, there is the advantage that ceramic bodies have agood sliding characteristic on metal in high vacuum, so that withcooling, the tube can displace itself with respect to the spacer when itundergoes changes in length. So that a vacuum having a residual pressureof about torr can be attained in the intermediate spaces between thetubes 4 and 5 and 5 and 7 for obtaining thermal insulation, it is alsoadvantageous that the ceramic materials have a low vapor pressure andtherefore emit practically no gases. ln addition to ceramic material,there are synthetic materials which can be used for the spacers,especially polyamides such as nylon.

To those skilled in the art it will be obvious upon a study of thisdisclosure that our invention permits of various modifications and maybe given embodiments other than particularly illustrated herein, withoutdeparting from the essential features of he invention and within thescope of the claims annexed hereto.

We claim:

1. A coaxial arrangement of tubular members for cryogenically coolablecables or the like, comprising inner and outer tubular members forming alongitudinally extending, annular interspace between each other, atleast one of said tubular members being contactable by coolant passingthrough the cable, and spacer structure of poor heat-conducting materialdisposed in said interspace and contacting said respective tubularmembers at small areas as compared with the noncontacted surface areas,said spacer structure having a ring portion surrounding the inner one ofsaid tubular members, said ring-shaped portion having inwardly directedand angularly spaced protrusions facing and contacting said innertubular member, and three spoke members joined with and protruding in aradially outward direction from said ring portion toward engagement withthe inner periphery of the outer tubular member, said three spokemembers being about 120 peripherally spaces from each other.

2. In a coaxial arrangement according to claim 1, said protrusions beingabout peripherally spaced from each other, and said spoke members beingangularly spaced about 60 from said protrusions.

3. In a coaxial arrangement according to claim 1 said protrusionsforming bosses integral with the material of said ring portion.

4. In a coaxial arrangement according to claim 3, said spoke membersconsisting of material integral with that of said ring portion.

5. In a coaxial arrangement according spacer structure consisting ofthree peripherally sequential component parts of which each extends overone-third of the inner-tube periphery, each of said three parts havingone of said respective spoke members.

6. In a coaxial arrangement according to claim 5, each of said threecomponent parts of said spacer structure comprising two ring elementsextending peripherally along about onethird of the inner-tube peripheryin axially spaced relation to each other, and two bridge elementsextending parallel to the tube axis and joining said two ring elementsat the respective ends there, said ring elements and said bridgeelements conjointly forming said ring portion, said spoke member beingsubstantially V-shaped and having its two legs joined with said two ringelements respectively so as to have the V-shape pointing away from saidring elements.

7. In a coaxial arrangement according to claim 6, said V- shaped spokemember having said legs extending from the middle of said respectivering elements.

8. In a coaxial arrangement according to claim 6, said V- shaped spokemember having a tip portion shaped substantially as a rounded knife edgewhere it engages said outer tubular member.

9. In a coaxial arrangement according to claim 6, each of said twobridge elements of said ring portion having two axially spaced bosseswhich form said inwardly directed protrusions respectively one of saidtwo bridge members having a marginal notch along its axially extendingend, and said other bridge member having a projection along its axiallyextending end, whereby said notch and projection of respectiveperipherally adjacent rings are in tongue-and-groove engagement witheach other.

10. In a coaxial arrangement according to claim 5, and band meansfastening said component parts of said spacer structure upon said innertubular conductor.

to claim 1, said

1. A coaxial arrangement of tubular members for cryogenically coolablecables or the like, comprising inner and outer tubular members forming alongitudinally extending, annular interspace between each other, atleast one of said tubular members being contactable by coolant passingthrough the cable, and spacer structure of poor heat-conducting materialdisposed in said interspace and contacting said respective tubularmembers at small areas as compared with the noncontacted surface areas,said spacer structure having a ring portion surrounding the inner one ofsaid tubular members, said ring-shaped portion having inwardly directedand angularly spaced protrusions facing and contacting said innertubular member, and three spoke members joined with and protruding in aradially outward direction from said ring portion toward engagement withthe inner periphery of the outer tubular member, said three spokemembers being about 120* peripherally spaces from each other.
 2. In acoaxial arrangement according to claim 1, said protrusions being about120* peripherally spaced from each other, and said spoke members beingangularly spaced about 60* from said protrusions.
 3. In a coaxialarrangement according to claim 1 said protrusions forming bossesintegral with the material of said ring portion.
 4. In a coaxialarrangement according to claim 3, said spoke members consisting ofmaterial integral with that of said ring portion.
 5. In a coaxialarrangement according to claim 1, said spacer structure consisting ofthree peripherally sequential component parts of which each extends overone-third of the inner-tube periphery, each of said three parts havingone of said respective spoke members.
 6. In a coaxial arrangementaccording to claim 5, each of said three component parts of said spacerstructure comprising two ring elements extending peripherally alongabout one-third of the inner-tube periphery in axially spaced relationto each other, and two bridge elements extending parallel to the tubeaxis and joining said two ring elements at the respective ends there,said ring elements and said bridge elements conjointly forming said ringportion, said spoke member being substantially V-shaped and having itstwo legs joined with said two ring elements respectively so as to havethe V-shape pointing away from said ring elements.
 7. In a coaxialarrangement according to claim 6, said V-shaped spoke member having saidlegs extending from the middle of said respective ring elements.
 8. In acoaxial arrangement according to claim 6, said V-shaped spoke memberhaving a tip portion shaped substantially as a rounded knife edge whereit engages said outer tubular member.
 9. In a coaxial arrangementaccording to claim 6, each of said two bridge elements of said ringportion having two axially spaced bosses which form said inwardlydirected protrusions respectively one of said two bridge members havinga marginal notch along its axially extending end, and said other bridgemember having a projection along its axially extending end, whereby saidnotch and projection of respective peripherally adjacent rings are intongue-and-groove engagement with each other.
 10. In a coaxialarrangement according to claim 5, and band means fastening saidcomponent parts of said spacer structure upon said inner tubularconductor.